FIG. 1 illustrates a structure of a wireless access protocol for transmitting data in a wireless interval of a universal mobile telecommunication system (UMTS) which is a 3rd generation mobile communication system. A data link layer corresponding to a second layer L2 of an open system interconnection (OSI) reference model includes a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a broadcast/multicast control (BMC) layer. A physical layer corresponds to a first layer L1. Information exchange between protocol layers is made through a virtual access point of a service access point (SAP). Parts indicated by ellipses in FIG. 1 correspond to SAPs. A unit of data transferred between the respective layers is denominated by different names according to layers and this is called a service data unit (SDU). A basic unit used to transmit data by a protocol is called a protocol data unit (PDU). Hereinafter, data transferred between the layers in the structure of the radio access protocol represents a data block of a prescribed unit such as the above-described SDU or PDU.
The MAC layer which is in charge of mapping between a logical channel and a transport channel selects an appropriate transport channel to transmit data transferred by the RLC layer and adds necessary control information to a header of a MAC PDU. The MAC layer performs a radio resource management function and a measurement function. The radio resource management function controls data transmission by setting an operation of the MAC layer based on a variety of MAC parameters transmitted by a radio resource control (RRC) layer, rather than being performed by the MAC layer itself. For example, the radio resource management function is to change a mapping relationship between the logical channel and the transport channel, or to multiplex data by a scheduling function and transmit the multiplexed data. The measurement function is to measure the traffic amount of a terminal and report the measured amount to an upper layer. The upper layer can change configuration of the MAC layer based on the measured information of the terminal by the MAC layer and can efficiently manage radio resources.
The RLC layer is located at an upper side of the MAC layer and supports reliable data transmission. The RLC layer segments and concatenates RLC SDUs transmitted by the upper layer to construct data of a proper size suitable for a radio section. The RLC layer of a receiving side supports a re-combination function of data to restore original RLC SDUs from the RLC PDUs. Each RLC entity may operate as a transparent mode (TM), an unacknowledged mode (UM), or an acknowledged mode (AM) according to processing and transmitting types of the RLC SDU. If the RLC entity operates as the TM, no header information is added to the RLC SDU transferred from the upper layer and the RLC SDU is transferred to the MAC layer. If the RLC entity operates as the UM, the RLC SDUs are segmented and concatenated to construct the RLC PDUs, and header information including a sequence number is added to each RLC PDU. However, the UM does not support data re-transmission. If the RLC entity operates as the AM, the RLC PDUs are segmented and concatenated to construct the RLC PDUs and can re-transmit data when packet transmission fails. For a re-transmission function of the AM, various parameters and variables are used such as a transmission window, a reception window, a timer, a counter, etc.
The PDCP layer is used only in a packet exchange region and may transmit data by compressing a header of an IP packet so as to increase the transmission efficiency of packet data in a radio channel. The PDCP manages a sequence number to prevent data from being lost during relocation of a serving radio network controller (SRNC).
The BMC layer broadcasts a cell broadcasting message transferred by a core network to users through a common channel.
The physical layer of the first layer provides an information transfer service to the upper layer by using a physical channel. The physical layer is connected to the MAC layer through the transport channel and data between the MAC layer and the physical layer is transferred through the transport channel. Data between different physical layers, that is, between a physical layer of a transmitting side and a physical layer of a receiving side is transferred through the physical channel.
The RRC layer located at the lowermost side of a third layer is defined only in a control plane and controls the logical channel, the transport channel, and the physical channel in association with configuration, re-configuration, and release of radio bearers (RBs). The RB means a service provided by the second layer to transfer data between networks including a terminal and a base station. The control plane indicates a layer structure transferring control information in a vertical structure of the wireless access protocol of FIG. 1. A user plane represents a layer structure transmitting user information such as data information. Next, a voice call service using the wireless access protocol of FIG. 1 will be described.
Voice data generated through, for example, an adaptive multi-rate (AMR) codec has a specific characteristic. The voice data is divided into a talk spurt and a silent period. The talk spurt means a voice data period generated while a user is actually talking and the silent period is a voice data period generated while a user is not talking. A voice data block which is a voice packet including voice data in the talk spurt is generated at a specific period (for example, every 20 ms). A silent data block which is a silent packet including voice data in the silent period is also generated at the same or different period as the specific period of the voice data block (for example, every 160 ms). To use such a voice service, radio resources for an uplink and a downlink should be allocated. The base station recognizes a necessary downlink resource by itself and transmits data to the downlink by using the downlink resource. However, the radio resources for the uplink and downlink should be assigned to the terminal by the base station to transmit and receive data. Such radio resource assignment information (for example, location of a corresponding frequency, a time unit, etc.) is called scheduling information and a technique of allocating the radio resources is called a scheduling method.
If a persistent scheduling method which is a kind of the scheduling method is used for a voice call, the base station sets the radio resources suitable for the talk spurt. That is, by using a characteristic that the voice data block is generated at a first period, for example, 20 ms, the base station previously sets the radio resources for transmitting and receiving uplink or downlink data to the terminal at intervals of 20 ms in a call setup process. The terminal receives the downlink data or transmits the uplink data by using the previously set radio resources at intervals of 20 ms. If the state of the terminal is changed from the talk spurt to the silent period, since the silent data block is generated at a second period (for example, every 160 ms), a considerable amount of radio resources allocated at intervals of 20 ms are wasted.
Similarly, if the state of the terminal is changed from the silent period to the talk spurt in the case where the base station previously allocates the radio resource to the terminal suitably for the silent period at intervals of 160 ms according to the persistent scheduling method, the terminal has lots of voice information to be transmitted but has a little amount of resources allocated. Therefore, transmission of voice information is delayed.